The present invention relates to an adapter for connecting a plastic pipe system to a metallic pipe system so as to provide a pressure seal and restraint against axial pull-out. More specifically, the present invention relates to an adapter for connecting a plastic pipe system to a metallic pipe system in which the end of the adapter, connectable to the metallic pipe system, is reinforced. In another aspect the present invention relates to a pipeline structure comprising a plastic pipe system and a metallic pipe system coupled by an adapter.
In pipeline structures, it has become rather common practice to utilize metallic pipe systems for a portion of the piping service and plastic pipe systems for other portions. One problem encountered in such piping systems is the difficulty of connecting the plastic pipe system to the metallic pipe system. While plastic pipe can be connected to other plastic pipe by gluing or melt fusion and metallic pipe can be joined to another metallic pipe by welding or clamping with appropriate gaskets, the relatively simple expedients such as melt fusion and welding cannot be used for connecting a plastic pipe system to a metallic pipe system. Consequently, clamping of the sections of the plastic pipe system to the metallic pipe system has been found to be the only reliable means of connection available. A wide variety of fittings and adapters for connecting a plastic pipe system to a metallic pipe system have heretofore been proposed. One problem in such coupling systems is the inability to attain a leakproof connection, particularly where gas or water under pressure is to be transmitted through the system, as when utilizing a metallic pipe system for the main of a natural gas distribution system and plastic pipe for branch systems therefrom.
Usually a coupling or adapter is made primarily from plastic so that it may be melt fused to the plastic piping system. In order to appropriately couple the plastic adapter or coupling to the metallic pipe system, the prior art has provided a number of rather complex and expensive fittings for both the plastic adapter and the metallic pipe system to which it is to be attached. Since pressure in a radial direction is normally applied to the plastic adapter or coupling in order to provide a fluid-tight clamped joint, the application of such pressure often results in distortion, cracking or other damage to the plastic coupling or adapter. Additionally, where the plastic adapter is made of polyethylene, there are difficulties in maintaining a fluid-tight seal because such plastic adapters can contract and pull out from the clamped joint.
It is therefore an object of the present invention to provide an adapter for connecting plastic pipe systems to metallic pipe systems which overcomes the above-mentioned difficulties of the prior art devices.
Another object of the present invention is to provide a simple and inexpensive adapter for coupling a plastic pipe system to a metallic pipe system and, more particularly, to provide a polyethylene plastic adapter for coupling a polyethylene plastic pipe system to a metallic pipe system.
Another object of the present invention is to provide an adapter for coupling a plastic pipe system to a metallic pipe system which can be connected to the plastic system by simple melt fusion and to the metallic pipe system by a simple clamping system.
Yet another object of the present invention is to provide a plastic adapter for connecting a plastic pipe system to a metallic pipe system which can be coupled to the metallic pipe system by clamping without damage to the adapter.
Another and further object of the present invention is to provide an adapter for coupling a plastic pipe system to a metallic pipe system which provides a leakproof junction for service in the transport of gas or water under pressure, especially when the plastic pipe system and plastic adapter are formed from polyethylene. These and other objects and advantages of the present invention will be apparent from the following description.